. COASTS VISITED BY THE AECTIC EXPEDITION. 607 



the equatorial regions. The true Nautilidee and Orthoceratidse are 

 essentially Palaeozoic. The latter, through two genera (Orthoceras 

 and Cyrtoceras), survived or lived on to Mesozoic times, dying out in 

 the Triassic seas. No Dibranchiate Cephalopod has yet occurred or 

 been found in any group of Palaeozoic rocks ; but the oldest of the 

 two sections in this order (the Decapoda) contains the extinct family 

 Belemnitidse, commencing in the Trias and ranging up to the close 

 of the Cretaceous period. Pew if any Octopoda are known fossil. 



The Silurian rocks of Bohemia, the British islands, Scandinavia, 

 and America have yielded nearly 2000 species of Tetrabranchiata, 

 America alone 450. We must probably, therefore, look to the 

 American continent for the source of the Cephalopod fauna of the 

 Palaeozoic rocks constituting the shores of the Arctic seas. Hitherto 

 only eight species have occurred in Arctic America, viz. one Cyrto- 

 ceras, one Lituites, five OrtTiocerata, and one Actinoceras. I am 

 now able to add three more species to the list of Arctic Tetra- 

 branchs — two Orthocerata and one Cyrtoceras. There are other 

 fragments which probably would illustrate more had the materials 

 been better. 



Bohemia exceeds all areas in having yielded to the researches of 

 Barrande no fewer than 830 species of Silurian Tetrabranchiate 

 Cephalopoda. 



Genus Oethoceeas, Breynius, 1732. 



Oethoceeas imeeicatttm, "Wahlenberg. 



Orthoceratites imbricatus, Wahlenb. Nova Acta Upsal. 1827, p. 89. 

 Orthoceras imbricatum, Hall, Pal. N. Y. vol. ii. p. 291, t. 61, 62 ; 

 Siluiia, t, 29. f. 7. 



A vertically divided half or completely crushed specimen of an 

 Orthoceras from Cape Louis Napoleon I refer to Orthoceras imbri- 

 catum. It occurs in the Niagara group of North America, and 

 in the Ludlow series of Wales. Our specimen measures 4 inches 

 in length ; but the diameter appears increased, owing to flattening. 

 Nothing can be determined as to the position or nature of the 

 siphuncle, owing to the crushed state of the shell. 



Loc. Cape Louis Napoleon, lat. 79° 38' ; east of Dobbin Bay, 

 Grinnell Land. 



Another specimen (marked D 12'), from the Upper Silurian of 

 Dobbin Bay, I take to be the same species. This shows the internal 

 portion, where the concave septa correspond in distance to those in 

 the weathered outer portion of the vertical half above described. 

 Pour other portions from Offley Island I also refer to O. imbricatum ; 

 they are considerably smaller, but in every other particular are the 

 same. 



Loc. Offley Island, lat. 81° 16', in white limestone. Cape Louis 

 Napoleon, lat. 79° 38'. Upper Silurian. 



Q.J.G.S. No. 135. 2 s 



